Method for detachably securing an insole to the bottom of a shoe last



Sept. 11, 1962 B. REID ETAL 3,052,904

J. METHOD FOR DETACHABLY SECURING A NSOLE TO TH OTTOM OF A SHOE LA edNOV. 3, 1961 FIGJ. FIG. 4.

4 54- IO l6 /l8 $5 F1612. FIG.5.

FIG. Z

JOHN B.REID

INVENTORS ROBERT A. SPENCE ATTORNEYS United States 3,052,904 METHOD FORDETACHABLY SECURING AN INSQLE T TIE BOTTOM 6F A SHOE LAST John B. Reid,Brighton, and Robert A. Spence, South Lincoln, Mass, assignors to BainCorporation, Cambridge, Mass, a corporation of Massachusetts Filed Nov.3, 1961, Ser. No. 150,037

3 Claims. (Ci. 12142) This invention generally relates to themanufacture of footwear, and more particularly to a novel method andmeans for temporarily securing a shoe insole to the bottom of a last asa step in the manufacturing procedure. This applications is acontinuation-impart of our copending application Serial No. 724,630,filed March 28, 1958, now abandoned.

In the past, insoles have customarily been secured to the bottom of awooden last by means of suitable tack fasteners driven directly throughthe insole into the last in order to temporarily secure the same inassembled alignment until completion of the lasting operation. Thedisadvantages of such a procedure are readily apparent. Each tack mustbe individually applied and subsequently removed, either manually or bya mechanical puller, with the resultant destructive marring or gougingof the insole. Occasional shearing of the conventional tack headnecessitates separate inspection of each shoe for the purpose ofdetecting and removing the embedded point. The exposed foot-contactingsurface of the insole is often damaged by seepage of the bottom fillerthrough the individual tack holes. Moreover, continuous insertion andremoval of tacks results in permanent mutilation and eventualdestruction of the wooden last.

The desirability of replacing the customary tack fastener with someother means to temporarily secure the insole to the last bottom has longbeen recognized by the industry. For example, the insole can be directlybonded to the last bottom by a thermoplastic adhesive which may besubsequently released through the application of either heat, asdisclosed by the patents to Blake, No. 1,3 65,221, and Brophy, No.2,520,995, or vibrational shock, as suggested in Nolan Patent No.2,701,887. In fact, other attempts to solve the problem have beenproposed but none have proved to be practical or acceptable to theindustry.

The difiiculties involved are understandable when the requirements of asuccessful solution are considered. Regardless of the means employed,the insole must be firmly retained in aligned position on the last so asto withstand the severe lateral stresses imposed during the lastingoperation that tend to transversely displace the insole. At the sametime, the temporary bond between the last and insole must be such thatupon completion of the lasting operation, it may be easily broken so asto completely release :the last for removal from the interior of theshoe without leaving any vestiges of the fastening means to eitherdiscolor or disfigure the foot-contacting surface of the insole.Further, the ultimate solution must be completely reliable and involveoperational costs competitive with those presently incurred in theutilization of the customary tack fastener.

It is therefore the primary purpose of this invention to directly afiixan insole to the last bottom without perforating the foot-contactingsurface of the insole or applying external heat to release athermoplastic bond.

The principal object of the present invention is the provision of anovel method and means for detachably securing an insole to the bottomof a last with double-faced pressure sensitive adhesive material inorder to prevent lateral displacement of the assembled components duringthe lasting operation while facilitating instantaneous re- 3,052,904Patented Sept. 11, 1952 lease of the adhesive bond when subjected to alongitudinal separating force. An equally important object of theinvention is to provide a method wherein the insole is superposed on thelast in aligned relation and the two are united merely by pressure by apressure sensitive adhesive material having opposed adhesive faceswhereby the unit may be employed without requiring trinnning of theinsole.

Other objects and the entire scope of the present invention will becomeapparent from the detailed description and by reference to theaccompanying drawings. It should be understood, however, that thedetailed description and specific examples, while indicating thepreferred embodiments of the invention, are given by way of illustrationonly, since various changes and modifications within the spirit andscope of the invention will become apparent as the description hereinprogresses.

Reference being made to the accompanying drawing which forms a parthereof, wherein like numerals refer to similar parts throughout, and inwhich:

FIGURE 1 is a side elevational view of a conventional last illustratingthe application of double-faced pressure sensitive adhesive tape to thebottom portion thereof.

FIGURE 2 is "a plan view of the last bottom shown in FIGURE 1;

FIGURE 3 is a side elevational view similar to FIG- URE 1 but furtherillustrating an insole detachably secured to the bottom portion of aconventional last by means of double-faced pressure sensitive adhesivetape;

FIGURE 4 is a plan View of a conventional insole illustrating theapplication of double-faced pressure sensitive adhesive tape to theinner last-contacting surface of the insole.

FIGURE 5 is a sectional view taken substantially along the line 55 ofFIGURE 4;

FIGURE 6 is a sectional view taken along the longitudinal center line ofa conventional insole illustrating a modified embodiment of the presentinvention wherein a removable protective strip is applied to the outeradhesive surface of the double-faced pressure sensitive adhesive tape;and

FIGURE 7 is a perspective view of the modified embodiment illustrated inFIGURE 6 with the protective strip partially withdrawn.

Referring now in detail to the drawings, the longitudinally extendingstrip of adhesive material, generally designated by the numeral 10,preferably is in the form of double-faced pressure sensitive tape havingopposed adhesive faces which may be applied either along the bottomportion 12 of a conventional last 14 or directly to the innerfoot-contacting surface 16 of a shoe insole 18, but preferably thelatter due to the relative planar configuration of the insole surface.In order to preserve the adhesive quality of the tape 10, a liner orstrip 20 may be employed for the protection of the outer adhesive face22 until such time as the insole and last are ready to be combined intoan assembled unit whereupon the protective strip is withdrawn, in themanner illustrated in FIGURE 7. Subsequent to the application ofadhesive material to either the insole or last, the latter componentsare thereafter positioned in superposed alignment with thelongitudinally extending strip of pressure sensitive tape 10 interposedbetween the insole foot-contacting surface 12 and last bottom 16 in themanner illustrated in FIGURE 3. Upon the application of externalpressure, which may be performed either manually or mechanically, atemporary adhesive bond is formed between the aligned components and theopposed adhesive faces of through the application of a longitudinalseparating force. This is normally accomplished by withdrawing the lastfrom the shoe after the heel portion 24 and toe section 26 have beencollapsed or broken about the pivotal joint 28 in the customary manner.Thereafter, the tape can be easily stripped from either componentwithout detrimental effect.

For the purposes of this disclosure, the term pressure sensitive servesto designate a distinct category of adhesive material which ispermanently tacky at room temperature and firmly adheres to a variety ofdissimilar surfaces upon mere contact with a minimum application ofpressure without leaving a residue upon removal. Preferably, theadhesive material contemplated by this invention is in the form ofdouble-faced pressure sensitive tape, as exemplified by the followingpatents: Kellgren Patent No. 2,206,899 of July 9, 1940, Kellgren et al.Patent No. 2,395,668 of February 26, 1946, Kellgren et al. Patent No.2,496,349 of February 7, 1950, Dahlquist et al. Patent No. 2,532,011 ofNovember 28, 1950, and

Marcin Patent No. 2,565,509 of August 28, 1951.

The adhesive material utilized to develop a releasable bond fordetachably securing the insole to the bottom of a shoe last preferablyis in the form of a double-faced pressure sensitive tape for convenienceof handling, applying, using and subsequent removal. The internalcohesive strength of the adhesive material must be greater than theadhesive bond established between the outer faces of the tape and theadjacent contacting surfaces of the insole and last, otherwisedelamination of the material will occur. Further, the pressure sensitivecharacteristics of the adhesive material utilized in this method serveto provide subsequent detachability of each of the aforementionedelements, one from another, during a later stage in the manufacture ofthe shoe, without requiring the application of either heat, cooling, ordestructive vibrational shock. In view of the severe stresses imposedupon the assembled insole and last during further operations in themanufacture of the shoe, it is apparent that the resultant adhesive bondbetween the insole and last must be capable of withstanding both tensileand shear forces, or a combination thereof until adhesion is no longerrequired. This is accomplished by the pressure sensitive adhesive whichserves to resist the forces imposed upon the bond between the insole andthe last.

For purposes of definition, the various terms used herein to describethe characteristics of the pressure sensitive tape are in accordancewith the standards specified by the Technical Commission of the PressureSensitive Tape Council, Glenview, Illinois, for Test Methods forPressure Sensitive Tapes appearing in Bulletin STC-l, issued September1955 and revised May 1959. Since adhesion generally signifies the bondproduced by the contact of a pressure sensitive adhesive to a surface onwhich it is applied, the force required to separate and remove thepressure sensitive adhesive at an angle normal to the surface of contactis commonly referred to as the peel adhesion characteristics of the tapewhile the lateral force which tends to misalign the insole and last in adirection parallel to the surface of contact is commonly designated asthe shear adhesion characteristic of the tape.

In this regard, the tensile adhesion strength of the tape in a directionnormal to the last must be sufficient to re tain the combined insole andlast in assembled relation and will depend upon (a) the length of tapeapplied, (12) the width of the applied tape, (0) the peel adhesion valueof the tape, and (d) an empirical factor k which is based upon suchitems as: the age and temperature of the tape as well as thetemperatures, cleanliness and finish of the insole and last surfaces. Arange in peel adhesion of between 15 ounces per inch and 75 ounces perinch, according to the Pressure Sensitive Tape Council Standards, willprovide adequate tensile adhesion to compensate for variations in (a),(b), and (d) above.

The shear adhesion strength of the tape must be sufficient to keep theinsole andthe last combined in fixed alignment and will depend upon (a)the length of the tape applied, (b) the Width of the applied tape, (0)the shear adhesion value of the tape, and (d) an empirical factor k,which is based upon the same conditions noted above. A range in shearadhesion of between ounces per square inch and 75 ounces per square inchwill provide adequate shear adhesion to compensate the variations in(a), (b), and (d) above.

Tape width usually varies from /2" to 1", with /1" width provingsatisfactory for the greatest number of sitnations encountered. Theresistance to normal and lateral or parallel forces on each side of thetape may be expressed as a function of the area of the tape, the tensileand shear adhesion values of the tape, and the empirical factor k:

wherein R is the resistance to normal and lateral forces on each side ofthe tape, tending to either separate or misalign the insole and thelast, A is the area of the tape, T is the minimum value of the peel orshear adhesion and K is an empirical constant defined above. Theadhesion strength of the tape necessary to hold a particular insole tothe last must result in a value of R which exceeds the combination offorces tending to separate the insole from the last. The mean area oftape necessary therefore varies with the values of T and K in theformula above. For example, a double-faced creped masking or draftingtape Scotch Brand #400 is satisfactory in many cases in lengths of 6" to8" when the width is A". Pressure-sensitive double-faced Scotch tape(non-creped cellophane base) has high peel and shear adhesive values.Therefore, the area can be substantially less utilizing this tape thanin the case of Scotch Brand tape #400, or other tape of equivalentmakes, and it is preferable for use in the manufacture of smaller sizedshoes or in the manufacture of shoes wherein the space between the weltribs or edges of the insole is relatively small. It is apparent thattapes possessing lower peel and shear adhesion values would utilize alarger area of tape and are easier to remove from the last or insole,but tapes possessing greater values of peel and shear adhesion withresulting smaller requirements of tape area are useful under particularcircumstances. The length and width of the tape can, of course, bevaried as can its lateral position on the insole or last. While a singlelongitudinally extending strip of pressure sensitive double-faced tapewill perform the desired results, a plurality of strips may also beemployed whenever desired without departing from the principles of theinvention. However, it should be pointed out that single faced pressuresensitive adhesive material cannot be used even if doubled upon itself,since it would exhibit no cohesive characteristics whatsoever.

The following examples illustrate the results achieved in the use ofdouble-faced pressure sensitive tape of varying peel adhesion values oninsoles formed from leather and Primes paper and a conventional woodenlast.

Example 1 A double face tape comprising a saturated crepe paper base 8mils thick had a listed Peel Adhesion of 30 ounces/ sq. inch. A test ofthe roll used showed figures as low as 22 ounces/sq. inch. The tape wasapplied to an insole and thereafter compressed with a shoe last. Thetape exhibited completely adequate adhesive characteristics.

Example 2 This example was conducted in the manner outlined in Example 1utilizing a double face tape comprising a rope paper 5.5 mils thick witha listed Peel Adhesion of 45 ounces/ sq. inch. The results werecompletely satisfactory.

Example 3 An attempt was made to find an adhesive material with 5 a PeelAdhesion too low to hold the insole to the last. A double face papertape with a listed Peel Adhesion of 7 ounces/ sq. inch (testing as lowas 2 ounces/sq. inch) was tried in the manner outlined in Example 1 andfound to adhere to the last but not to the insoles.

Example 4 The experiment outlined in Example 1 was repeated with adouble face glass tape with a listed Peel Adhesion of 70 ounces/sq.inch. The adhesive qualities were completely satisfactory and nodifficulty was experienced in removing the tape from the insole.

The Peel Adhesion values referred to were determined according to TestMethods for Pressure Sensitive Tapes developed by the Spec. andTechnical Commission of the Pressure Sensitive Tape Council, Glenview,Illinois, Bulletin STC-l, issued September 1955, revised May 1959.

The present invention will thus be seen to completely and effectivelyaccomplish the objects enumerated hereinabove. By applying double-facedpressure sensitive adhesive tape material to either the insol or thelast and thereafter aligning the elements in superposed relation, uponcompression the adhesive faces will detachably secure the same in fixedassembled relation until completion of the required lasting operations.Since the insole and last need only be temporarily united, subsequentseparation is possible upon exertion of a longitudinal face of the typecaused by removal of the last from the shoe after completion of thelasting procedure. It will be realized, however, that various changesand substitutions may be made to the specific embodiments disclosedherein for the purpose of illustrating the principles of this invention,Without departing from these principles. Therefore, this inventionincludes all modifications encompassed within the spirit and scope ofthe following appended claims.

What is claimed is:

1. A method for detachably securing an insole element of a shoe to thebottom portion of a shoe last element which comprises the steps ofapplying pressure sensitive adhesive material having opposed adhesivefaces to one of said elements merely by pressure, positioning saidelements in superposed aligned relation with the opposed adhesive facesof said pressure sensitive material disposed therebetween, merelycompressing said elements into intimate contact with said adhesivematerial to form an assembled unit having the elements atfixed inaligned relation by the opposed adhesive faces of said pressuresensitive material whereby the elements can thereafter be separatedwithout further treatment by stripping said material from either of saidelements.

2. The method of claim 1 wherein the adhesive material is applied firstto said insole element.

3. The method of claim 1 wherein the adhesive material is applied firstto the bottom portion of said last element.

References Cited in the file of this patent UNITED STATES PATENTS1,365,221 Blake Jan. 11, 1921 2,532,011 Dahlquist et a1. Nov. 18, 19502,635,363 Dorgin Apr. 21, 1953 2,659,912 Kamborian Nov. 24, 19532,865,097 Volbrath et a1 Dec. 23, 1958 2,985,970 McCarthy May 30, 1961

